Someone who -- them once said that Gabby Giffords and her husband mark Kelly we're simply America at its best. She once called the most positive person in congress he an astronaut the commander of the space shuttle. And then last January a stranger pulled out a gun and put a bullet through Gabby Giffords brain. Tonight you will see the astonishing journey from that moment until today what happens when everything changes. And what you love is put to the test. Their book is called -- a story of courage and hope and will Begin with mark Kelly reading his description. Of that spirited sunny high octane woman he married. Four years ago. And. -- -- -- Lives and yeah yeah. Udall wants an intellectual but -- this -- community advocate -- and everyone went on -- and cowgirl. -- -- Losing her hands as punctuation marks. Being here and say -- -- and former tennis shoes and started walking around the district an -- today. Every single person. And then on January -- These are the photos of the vibrant young congresswoman and her red suits talking to constituents in front of a supermarket. Seconds later 22 year old man three feet away -- and Glock nineteen. And aims the gun at her head. See we are following a developing story being -- any grocery store the coolest. He fires travels thousand feet per second through the entire left side of her brain. The fires thirty -- afterwards killing six people wounding thirteen. Before bystanders heroically tackle. Some of the first reports had -- done. CNN has confirmed that the congresswoman has been killed represented Giffords is in fact she was clinging to life. The -- camp outside her hospital strangers leaving tributes. Inside -- talk with her husband shuttle commander astronaut mark Kelly who told me. Even though she couldn't move speak -- opened her eyes he knew his wife and his wife -- fight her way back. You know telling them she's gonna make a 100%. Recovery -- real differences too tough. Let this -- here. So tough he thought maybe she'd already recognized him with one hand toying with his wedding ring the way she used to do. Four days later the president came to visitor after that her friends in congress walking in calling out her name. And a breakthrough room Gabby opened her eyes for the first time. -- his skin of her head of the bullet toward the length of her brain chattering her skull. And not be daunted by the odds against her less than 10% of people with brain injuries even survive. Kelly consulted with the doctors about the odds. -- the waste to defy them. Any lower it would've killed there. Any further. Mid line it would of kilter for -- hemispheres that would've killed or any further -- -- should never be able to speak again any higher should never be able to walk. But until tonight. All we knew of what happened inside her hospital rooms with that photograph of mark Kelly's hands in -- And that a veteran. Ask that his purple heart -- placed on her -- We had no idea privately Kelly was about to do something old and this -- your -- he had decided. He would videotape her recovers. So sure she would astonish skeptics and with trademark curiosity. Want to know what she'd been through -- just thought she's gonna ask okay what was all that like. Cameras recorded an unflinching portrait of what it is to struggle back after you've been shot in the head at point blank range. Here a photo of heard day one after the shooting here before. Then two weeks later after she's been moved to Houston those papers begins to roll your secret code named JS lasso. A woman went so animated -- slightly as if the bullet has embraced -- -- uses. Her husband writes he believes optimism is a form of healing hope it's a form of law you look great. Just got more work to do here. -- And remember how he insisted the -- consciously fingered their wedding rings. About hold up my ring. Let's show everybody mayor -- can you do that. -- When he -- my ring off. It -- your finger cures. About it -- Able to do that. Doing really well. -- -- ago. Good job. Mark Kelly searching for the woman he could not wait to see -- again her laugh her smile. -- -- -- Adolescents. That -- it as well it all that's better. At this point the scan shows they've been so much swelling and her brain they were forced to remove a piece of her skull the size of her palm. -- because she's always liked working toward goals he decides to different -- -- -- tennis -- sitting on the chair in the room. Here -- issues you're for a jog today six corporate. He told her somehow together in two weeks. -- -- get up and get her in those shoes and failure. It's not an option. -- well. Again it is two and a half weeks after the shooting. What the thumbs up. One -- here but this thing here. This war. Yeah that's it that's a thumb. About two fingers. -- and I do we thought it. -- -- And another little -- we -- there are the starts chanting a phrase and then choose up on the C word. He's had. And. Yes. He put the sign from visitors that says no crying. You write each morning when he walked into room. Told himself to take a deep breath -- Pope focus. Thinking this is -- -- wedding vows mean. -- sickness and in health clause that's real. And alone at night he writes in the book -- for bargain with god. And if she could never walk again. Please please. -- her home and smile. -- -- victory this program. And the miracle --

This transcript has been automatically generated and may not be 100% accurate.

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